mfd: cros_ec: Free IRQ automatically

Free the IRQ we might have requested when removing the cros_ec device,
so we can unload and reload the driver properly.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>